The present invention relates to glass panels provided with heat insulating performance and heat shielding performance optimal for use as windowpanes in buildings.
A need for the high heat shielding performance of the opening portions in a house has grown year by year. According to the standard of the performance indication for the double layer glass for use in houses presented by xe2x80x9cHigh Performance Glass Promotion Conference,xe2x80x9d it is required that the solar radiation heat gain ratio be 0.51 (this value means that the solar radiation heat of 51 units reaches the indoor space based on the solar radiation heat of 100 units) or below. Additionally, according to the next generation energy conservation standard publicized as an announcement from Ministry of International Trade and Industry and Ministry of Construction in March of 2000, it is required that the solar radiation heat gain ratio in any of the districts III, IV, and V be 0.49 (this value means that the solar radiation heat of 49 units reaches the indoor space based on the solar radiation heat of 100 units) or below, which ratio being more preferable.
As a measure for improving the heat shielding performance of the window portions of a house, the heat ray absorbing glass has come into use recently. For example, Japanese Patent Publication No. 6-94377 and Japanese Patent Publication No. 6-102557 disclose respective types of heat ray absorbing glass based on the combinations of special metal oxides.
Additionally, nowadays, double layer glass panels have been developed which have not only the heat shielding capability but also heat insulating capability. For example, Japanese Patent No. 2882728 discloses a double layer glass panel in which a sheet of colored heat ray absorbing glass is arranged on the outdoor side thereof, a sheet of clear type glass is arranged on the indoor side thereof, and a layer of low emissivity film is formed on the indoor side of the sheet of colored heat ray absorbing glass placed outside the room.
The above described double layer glass panel makes a too thick paned window glass, because it is necessary to acquire a thickness of 6 mm or more for the air layer (or a gas layer such as an argon gas layer) between the two sheets of glass, in order to acquire a heat insulating property. For example, when the thickness values of the glass sheets are each 3 mm, and the thickness of the air layer is 6 mm, the thickness of the windowpane amounts to even 12 mm, so that it can hardly be used in a common house. Accordingly, a vacuum glass panel has been developed which is provided with a very thin vacuum layer of the order of 0.2 mm in thickness interposed between the two sheets of plate glass being the same in constitution as those in the above described double layer glass panel.
This type of vacuum glass panel gives a sufficiently thin windowpane, and moreover suppresses the ingression of the solar radiation heat into the interior of a room in the hot summer daytime, and does not lose the coolness provided by a chiller against the exterior in the nighttime, so that the cooling efficiency is improved due to the effect of the heat ray absorbing glass and the low emissivity film. Additionally, this type of vacuum glass panel also improves the heating efficiency in winter, and hence comes into widespread use as an energy conservation type windowpane.
The above described type of vacuum glass panel has a weak point that it is warped on receiving the solar radiation. When the rigidity of the window sash is strong, no problem occurs; when it is not sufficiently strong, the sash frame is also warped by the effect of the glass panel warping, so that the operation of opening and closing becomes unsmooth, and there is a fear that in an extreme case the sash frames chafe against each other to be abraded by each other.
The mechanism of the warping can be interpreted as follows. When a windowpane receives the sunlight, the sheet of the heat ray absorbing glass on the outdoor side absorbs the solar radiation energy with the resulting temperature rise and thermal expansion. On the other hand, the indoor side sheet of plate glass is low in heat ray absorption function and in addition the solar radiation energy is absorbed by the heat ray absorbing glass, so that the temperature rises very slightly and accordingly the thermal expansion is very small. Additionally, the vacuum glass panel is composed of two sheets of plate glass with the peripheral portions thereof adhesively sealed and fixed using hard materials such as a low-melting glass and a solder. Accordingly, the difference in thermal expansion between the two sheets of plate glass gives rise to the wrapping on the basis of the same principle as that in bimetal.
Incidentally, in the double layer glass panel, a soft material is used as the adhesive sealing material, and accordingly the difference in thermal expansion between the two sheets of plate glass is absorbed by the deformation of the adhesive sealing material, without involving the generation of the warping.
An object of the present invention is to provide a glass panel in which heat insulating performance and heat shielding performance are so sufficient that no warping is generated even on receiving the solar radiation.
For the purpose of achieving the above described object, the heat insulating/heat shielding glass panel of the present invention is a heat insulating/heat shielding glass panel constituted so as to partition an indoor space and an outdoor space, by forming a gap layer with a predetermined spacing between a pair of sheets of plate glass, and a sealed periphery portion all along the peripheries of the two sheets of plate glass so that the gap layer is sealed into a reduced pressure state, in which a functional film having an emissivity of 0.20 or less is formed on the surface, in contact with the gap layer, of the outdoor side sheet of plate glass of the two sheets of plate glass; the solar radiation reflectance is 45% or less, the solar radiation absorptivity thereof is 25% or less; and the following relation holds: the solar radiation absorptivityxe2x89xa7(xe2x88x921.02)xc3x97the solar radiation reflectance+48.5 (the solar radiation gain ratioxe2x89xa60.51).
Additionally, as for the above inequality, the following alternative relation holds: the solar radiation absorptivityxe2x89xa7(xe2x88x921.11)xc3x97the solar radiation reflectance+52.5 (the solar radiation gain ratioxe2x89xa60.49).
FIG. 3 is a graph showing the relationship between the solar radiation absorptivity and the solar radiation reflectance; in a sheet of plate glass provided with a functional film 5 of the preset invention, the solar radiation reflectance thereof is 45% or less, the solar radiation absorptivity thereof is 25% or less, and the following relation holds: the solar radiation absorptivityxe2x89xa7(xe2x88x921.02)xc3x97the solar radiation reflectance+48.5. In this connection, for either the solar radiation absorptivity or the solar radiation reflectance, there are two modes: one is the absorptivity (or reflectance) as observed from the film surface side, and the other is the absorptivity (or reflectance) as observed from the surface of the sheet of plate glass, both being a little different from each other; in the present invention, any one of these two absorptivities (or reflectances) has only to satisfy the above inequality.
The grounds for the above numerical restrictions are as follows:
(1) In the range where the above inequality does not hold, the solar radiation heat gain ratio of 0.51 or less cannot be achieved.
(2) With the solar radiation absorptivity exceeding 25%, the effect of the present invention cannot be obtained, because the warping is generated owing to the increased temperature difference, on receiving the solar radiation, between the two sheets of plate glass. The solar radiation absorptivity is preferably 20% or less, and more preferably 15% or less.
(3) With the solar radiation reflectance exceeding 45%, the visible light reflectance is often and simultaneously increased so that the dazzling appearance due to reflection is augmented, and the plate glass concerned is not suitable for use as a windowpane in a house.
By adopting the above described constitution, the thermal expansion of the outdoor side sheet of plate glass when receiving the solar radiation can be suppressed, and the solar radiation heat gain ratio of 0.51 or less can be achieved.
FIG. 4 is a graph showing the relationship between the solar radiation absorptivity and the solar radiation reflectance; in a sheet of plate glass provided with a functional film 5 of the preset invention, the solar radiation reflectance thereof is 45% or less, the solar radiation absorptivity thereof is 25% or less, and the following relation holds: the solar radiation absorptivityxe2x89xa7(xe2x88x921.11)xc3x97the solar radiation reflectance+52.5. In this connection, for either the solar radiation absorptivity or the solar radiation reflectance, there are two modes: one is the absorptivity (or reflectance) as observed from the film surface side, and the other is the absorptivity (or reflectance) as observed from the surface of the glass plate, both being a little different from each other; in the present invention, any one of these two absorptivities (or reflectances) has only to satisfy the above inequality.
The grounds for the above numerical restrictions are as follows:
In the range where the above inequality does not hold, the solar radiation heat gain ratio of 0.49 or less cannot be achieved.
With the solar radiation absorptivity exceeding 25%, the effect of the present invention cannot be obtained, because the warping is generated owing to the increased temperature difference, on receiving the solar radiation, between the two sheets of plate glass. The solar radiation absorptivity is preferably 20% or less, and more preferably 15% or less.
With the solar radiation reflectance exceeding 45%, the visible light reflectance is often and simultaneously increased so that the dazzling appearance due to reflection is augmented, and the plate glass concerned is not suitable for use as a windowpane in a house.
By adopting the above described constitution, the thermal expansion of the outdoor side sheet of plate glass when receiving the solar radiation can be suppressed, and the solar radiation heat gain ratio of 0.49 or less can be achieved.
As the above described functional film displaying the above described characteristics, there can be proposed a constitution obtained by laminating a dielectric layer and a metal layer, for example, in such a way that a first dielectric layer, a metal layer, and a second dielectric layer are formed in the order of description on the surface of a sheet of plate glass; wherein the first dielectric layer is from 10 to 90 nm in thickness, the metal layer is from 10 to 18 nm in thickness, and the second dielectric layer is from 10 to 60 nm in thickness.